Questions and Answers

1.  When did the Cambrian period take place?

The Cambrian period began around 543 million years ago and ended around 490 million years ago.

2.  How was the start and end of this period determined?

The Cambrian period began with the retreat of the Proterozoic ice at the end of an ice age.  The period ended with many small mass extinctions, which were possibly caused by ocean temperature cooling, and culminated in a mass extinction which killed off a number of unique taxa.

3.  How were the continents arranged?

The single supercontinent Rodinia began to fragment into smaller continents which did not correspond to the continents of today.  The fragmented pieces of Rodinia were concentrated in the southern hemisphere.  Most of the land was still together in a single supercontinent called Gondwana.  Most of North America was a fragmented chunk of land known as Laurentia, which was west of Gondwana.  Siberia was also a separate continent east of Laurentia.  Present day Scandinavia, eastern Europe, and European Russia were on a single continent south of Laurentia called Baltica.  Large mountain ranges were being formed because of seafloor spreading, crustal subduction, and plate movement and collisions which generated pressure and heat and resulted in the folding, faulting, and crumpling of the earth.

4.  What was the climate like?

The climate was very mild.  There were no glaciers, and all land lay in warm tropical and temperate latitudes.  Because of the melting of large amounts of ice at the beginning of the period, the sea level rose significantly.  The beginning of the Cambrian period was also the first time that oxygen mixed into sea water in a significant quantity.  This occured because the number of oxygen-depleting bacteria decreased sufficiently to permit the oxygen levels to rise to that of today.  Because the dissolved oxygen was made available to animals, it is speculated that this is what caused the Cambrian Explosion.

5.  What were the dominant plants and animals?

During the Cambrian period, there were no plants.  But the animal population went through an event known as the Cambrian Explosion due to the vast number of new species which appeared.  Most major groups of animals first appear in fossils that are dated to this time period.  New species include:  echinoderms (starfish, sea cucumbers, brittle stars, sea urchins, e.t.c.), mollusks, annelids (worms), arthropods (spiders), onychophorans ("velvet worms"), poriferans (sponges), as well as many others.  Not only were animals becoming more diverse, but they were also developing new ecological niches and strategies such as active hunting, burrowing, and making complex branching burrows.

6.  Were there any mass extinctions?

Yes, near the end of the Cambrian period there were many small mass extinctions and a final mass extinction that marks the segway between the Cambrian and Ordovician periods.  The small mass extinctions mainly affected shallow warm-water species, therefore it is thought that ocean temperature cooling is the cause.  The end mass extinction killed of many species, including:  archaeocyathids (the first reef builders), Anomalocarids, many lobopods, trilobites, basal arachnomorphs (relatives of Crustacea), several orders of nautiloids, and many primitive echinoderms.  Glaciation and anoxia are the suspected causes of this mass extinction.

Links and Sources

http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.htm

http://www.ucmp.berkeley.edu/cambrian/camb.html

http://www.peripatus.gen.nz/paleontology/Cambrian.html

http://www.starsandseas.com/SAS%20Evolution/SAS%20geoltime/ geotime_cambrian.htm